Docs: warning marker isn't interpreted

> [!WARNING]
> At some point in the past the marker circled in the below screenshot was interpreted such that the quote below was in a yellow box with a ⚠️ pictogram, like this text. Looks like it broke at some point.

No file or test is named. Start by reproducing the quoted [!WARNING] Markdown example in the project's documentation renderer and trace how admonition markers are handled. Done means the quote renders as a yellow warning box with a warning pictogram, as shown in the issue.

Written by the indexing model from the issue text.